(a) Field of the Invention
The present invention relates to a method of manufacturing a semiconductor pn junction in a Group II-VI compound semiconductor, and more particularly it pertains to a method of manufacturing a ZnSe pn junction.
(b) Description of the Prior Art
Those Group II-VI compound semiconductors such as ZnS and ZnSe have a relatively large energy band gap. Light-emitting diodes (hereinafter abbreviated as LED) made of Group III-V compound semiconductors such as GaAs have their peak intensity of light emission at about 5500 A at the maximum, and they are unable to emit light in a region of wavelength shorter than that. If, however, it is possible to form a pn junction by the use of a semiconductor material selected from Group II-VI compound semiconductors having large energy band gaps, there will be obtained LEDs having a light-emission wavelength range whose peak intensity is shorter than about 5500 A which, in terms of color in the visible light wavelengths, ranges from blue-green to blue-violet. Thus, it would be possible to manufacture luminescing semiconductor devices capable of emitting colored lights and also possible to expand the fields of application of such an LED.
However, it has been extremely difficult so far to form a pn junction with a semiconductor material selected from a group II-VI compound semiconductor by relying on the conventional methods in the current level of techniques.
More specifically, in the current level of techniques, it is possible to easily obtain, either through the doping of a donor impurity or through heat-treatment in a vapor such as Zn, an n type crystal portion from Group II-VI compound semiconductors such as ZnSe, CdS and ZnS.
However, the circumstances differ drastically if one wishes to obtain a p type crystal in such semiconductor materials as those mentioned above. That is, even when efforts are made to obtain a p type crystal by doping an acceptor impurity, i.e., more specifically by doping, at the time of crystal growth, an acceptor impurity to form a p type, or to change a portion of an n type Group II-VI crystal into a p type by either doping, through diffusion or as an alloy, an acceptor impurity into an n type Group II-VI crystal, still the resulting crystal remains to be an n type Group II-VI crystal or becomes a crystal close to an insulator having a very high resistivity, so that a useful desirable p type region crystal has not been obtained. Thus, it has not been possible to manufacture a pn junction which causes injection luminescence in a Group II-VI compound semiconductor according to the prior art.
The reason for it not being possible to obtain a p type semiconductor crystal portion in a Group II-VI compound semiconductor crystal according to the prior art is because of the fact that, when an acceptor impurity is introduced to obtain a p type crystal, defects develop, within the crystal. These defects function as a donor in accordance with the amount of the acceptor impurity which is introduced in the crystal, with a natural trend to establish a stable-state thermodynamically, causing the development of compensation of acceptor carriers. This development of carrier compensation is called a "self-compensation phenomenon". Those defects developing within the crystal which function as the donor consist, for example, of Se vacancies which develop due to the escape of Se atoms out of the crystal, said escape taking place because, in a compound semiconductor such as ZnSe, Se atoms have a higher vapor pressure than Zn atoms, and because, for this reason, Se atoms easily escape out of the ZnSe crystal. Such defects also include a complex of Se vacancies with the doped impurity. These defects, i.e., Se vacancies and/or complexes with Se vacancies and impurity, function as a donor.